Rebel fighters loyal to renegade General Laurent Nkunda seized an army base 3 km (2 miles) from the ranger station at Rumangabo during an artillery battle with government troops in Democratic Republic of Congo's eastern North Kivu province.

The station is in the southern half of the Virunga National Park, located on the border with Rwanda and Uganda and home to around 200 of the world's 700 surviving mountain gorillas.

"We need to evacuate the rangers and their families because there is a real threat that the conflict may engulf the main park station," park spokesperson Samantha Newport told Reuters.

Between 30 and 50 rangers were waiting to be extracted from Rumangabo late on Wednesday. Many have been living there since Nkunda's insurgents invaded much of the park last September.

"It's incredibly serious. The future is entirely uncertain. It will be impossible for the rangers to do their job if the station is overrun," Newport said.

In the past decade, 120 Virunga park rangers have been killed in clashes with armed groups and poachers.

Around 10 mountain gorillas were slaughtered last year in the Virunga reserve, shocking conservationists and causing a stir even in a country where violence, hunger and disease kill 1,500 people a day in the aftermath of a 1998-2003 war.

Around 100,000 civilians have fled their homes in North Kivu since fighting between the government army and Nkunda's rebels broke out in August after the collapse of a January peace deal.

Doctors at a hospital run by charity Medecins Sans Frontieres (MSF) treated dozens of soldiers and civilians injured in Wednesday's mortar, rocket and tank fire.

"We have two surgery teams working full-time ... This is enormous today," said MSF mission chief Anne Taylor. "Over the past few weeks the conflict has turned into a full-scale war."

A military spokesman for the United Nations mission in Congo (MONUC) said U.N. peacekeepers had come under direct fire from Nkunda's fighters. The mission deployed armoured vehicles and helicopters to the area of the clashes.